1. Field of the Invention
The present invention relates to a robot apparatus capable of diagnosing the state of a speed reducer formed in each joint of a multi-joint robot, and a multi-joint robot speed reducer state diagnosing method.
2. Description of the Related Art
Conventionally, various robot apparatuses have been used in factories and the like, and robot apparatuses including multi-axis, multi-joint robotic arms in order to perform more complicated operations have widely spread in recent years.
In a robot apparatus for performing a complicated operation as described above, the degree of freedom of the operation of a robotic arm is high. During the operation, therefore, the robotic arm may be damaged by contacting another object such as a surrounding structure, work, or tool. For example, if the robotic arm collides against, e.g., a surrounding object and a shock is applied to a speed reducer of an actuator formed in a joint, the speed reducer may cause damage such as ratcheting. If the speed reducer is damaged, the angle transfer accuracy of the joint decreases, and this decreases the operation accuracy of the robotic arm. Recently, therefore, various techniques have been proposed against the collision of the robotic arm.
For example, a technique in which an angle detector is installed on each of the input side and output side of an actuator (a motor and speed reducer) of each joint of the robotic arm, whether a collision has occurred is determined from a detected angle difference, and the robotic arm is driven in the opposite direction if it is determined that a collision has occurred has been proposed (see Japanese Patent Application Laid-Open No. 2010-228028).
The technique described in Japanese Patent Application Laid-Open No. 2010-228028 can detect the occurrence of contact of the robotic arm. Since, however, a speed reducer is difficult to visually check from the outside, it is impossible to know the degree of damage inflicted to a speed reducer by contact. To determine damage to a speed reducer, therefore, it is necessary to check the tooth surface of a gear by disassembling the speed reducer, and determine the necessity of replacement. To determine damage to a speed reducer by disassembling, however, the speed, reducer must be removed from the robotic arm and disassembled, and this requires a long time.
On the other hand, a technique in which a driving torque obtained from the value of a driving current to an actuator of each joint and an estimated torque obtained from a command position and torque fluctuation parameter are compared and the necessity of replacement is determined based on the torque difference has been proposed (see Japanese Patent Application Laid-Open No. 2007-301680).
Unfortunately, the technique described in Japanese Patent Application Laid-Open No. 2007-301680 lacks accuracy because a torque value to be used in abnormality detection is obtained by estimation by calculations from various parameters (e.g., a servo gain, the weight and barycenter of the robotic arm, and a parameter having influence on the driving torque of a servo motor).
Accordingly, the present invention provides a robot apparatus and multi-joint robot speed reducer state diagnosing method capable of accurately determining the state of a speed reducer of a multi-joint robot within a short time.